This invention relates to the use of demeclocycline and other tetracycline derivatives for use in lowering intraocular pressure when applied to the eye.
The term "glaucoma" refers to a group of eye diseases affecting some 2% of the adult population. It is one of the three leading causes of acquired blindness in the developed world. Glaucoma develops because the pressure inside the eye (the intraocular pressure) becomes elevated above a level that can be tolerated safely. Within the eye, the ciliary processes secrete a clear fluid called aqueous humor. This field is essential for the nutrition of the lens and cornea of the eye. This aqueous humor drains through the trabecular meshwork, against a moderate resistance. The circulation and resistance to drainage of this fluid generates the intraocular pressure. Such intraocular pressure maintains the round shape of the eye and thus, provides for the eye's exquisite optical properties.
In glaucoma, a reduction in the drainage of aqueous humor elevates the intraocular pressure above normal level; this elevated intraocular pressure is transmitted throughout all tissues in the eye. The optic nerve, responsible for carrying the visual image from the light-sensitive retina to the brain, is damaged in glaucoma secondary to the elevated intraocular pressure. Because of impaired blood circulation and/or mechanical deformation that results from the abnormal pressures, the optic nerve undergoes an atrophic process and vision subsequently is reduced.
The various therapeutic approaches to glaucoma involve efforts to lower intraocular pressure either by reducing the rate at which aqueous humor is formed or by increasing the rate at which it leaves the eye. In the developed world where medications are accessible, the first approach to glaucoma therapy utilizes one or more drugs to achieve this result. When therapy with medications fails to lower intraocular pressure adequately, laser therapy or conventional surgical therapy is used next.
A wide range of medications now are available to treat glaucoma. Some are administered topically as drops to the eye; others are systemic medications taken orally in pill form. In many but not all glaucoma patients, these medications can lower intraocular pressure to a safe range.
All available glaucoma medications have certain limitations. First, both topical and systemic medications have significant ocular side effects, depending on the specific drug. These include such problems as local irritation, drug-induced changes in the refractive error of the eye, and increased risk of retinal detachment. Some medications make the pupils so small that they limit light entrance into the eye and cause difficulty with vision.
Systemic side effects also are prominent in some patients. Medications currently in use may alter serum electrolytes, appetite, mental status and the like. Even some medications used topically as drops can be absorbed into the blood and cause serious systemic side effects in susceptible individuals. Examples of side effects from drop therapy include extra heartbeats, cardiac failures, gastrointestinal symptoms and exacerbation of underlying asthma. All anti-glaucoma medications have limited duration of action; both topical and systemic medications require application at least once daily, and some require four times a day usage.
Because of ocular/systemic side effects and the limited duration of action, a major problem in the use of anti-glaucoma medications is poor patient "compliance". The term "compliance" refers to the tendency of patients to use their medications as instructed by the physician.
Because of the proved effectiveness of anti-glaucoma drug therapies and because of the higher risks of laser and surgical therapies, the search continues for new drugs to treat glaucoma.